Multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy is a variant of chronic acquired demyelinating polyneuropathy. A 65-year-old women presented with upper arm weakness. A nerve conduction study showed conduction blocks over intermediate segments with sparing of distal compound action potentials. Magnetic resonance imaging revealed asymmetric hypertrophy of the brachial plexus on the affected side. These findings represent important electrophysiological and radiological evidence of MADSAM neuropathy. The condition of the patient began to improve after starting intravenous immunoglobulin administration.